UPDATE: 4/17/13 1:50 PM ET
Possible leads on suspect
Follow GlobalPost's Day 3 Live Blog on the Boston Marathon bombing for more updates.
UPDATE: 4/16/13 7:00 PM ET
As the second day after the bombings at the Boston Marathon draws to a close, the death toll still stands at 3, with more than 180 people having received treatment at area hospitals for injuries. At least 17 people remain in critical condition.
The authorities still do not have anyone in custody, according to the latest updates.
We will be closing our live blog coverage for the night, but please check here for recent developments.
UPDATE: 4/16/13 6:05 PM ET
Obama to visit Boston Thursday
President Barack Obama will visit Boston on Thursday to speak at a memorial service for victims and survivors of the marathon bombings, the White House said.
UPDATE: 4/16/13 5:45 PM ET
UPDATE: 4/16/13 5:32 PM ET
UPDATE: 4/16/13 5:05 PM ET
New details emerge about bombs used
New details have emerged about the type of bombs used in Monday’s attack on the Boston Marathon.
Sources are telling the media that at least one bomb, and possibly two, were “pressure cooker” bombs – explosive devices made by stuffing black powder or gunpowder (the explosive) and nails and ball bearings (to cause maximum harm) into metal pressure cookers, which are found in many American kitchens.
The US Department of Homeland Security warned about such bombs in a 2004 memo entitled “Potential Terrorist Use of Pressure Cookers,” CBS News noted.
While the crudeness of such a bomb – and the fact that you can find instructions on how to assemble one on the Internet – might indicate that an amateur was behind the attack, the Boston-based Christian Science Monitor cautioned readers not to jump to that conclusion.
According to the Christian Science Monitor:
Islamist extremists in France tried to use pressure cookers last year in what officials there said could have been the biggest terror attack on French soil in years, until it was foiled. Likewise, US Army Pfc. Naser Abdo, who was convicted in 2012 of plotting to bomb a Texas restaurant where Fort Hood soldiers regularly ate, got the recipe for a pressure cooker bomb from an Al Qaeda website.
UPDATE: 4/16/13 4:22 PM ET
Boston's imam: "We're Bostonians"
The imam who leads Boston's largest mosque, the Islamic Society of Boston Cultural Center, voiced his concern in the wake of the explosions yesterday.
"We're Bostonians - we mourn with the city," said Suhaib Webb, according to The Huffington Post. "We stand in support with the city, with the victims. We're hurt, equally shocked and equally pissed off."
Intelligence officials also told lawmakers on Tuesday that the Saudi national injured during the bombings was no longer a person of interest and had been cleared.
After being briefed by Director of National Intelligence James Clapper, Republican Sen. Saxby Chambliss said, "He was never categorized as a suspect; he was a person of interest. My understanding is that he totally cooperated and that he is no longer a person of interest."
Read more at Foreign Policy.
UPDATE: 4/16/13 3:00 PM ET
Breakdown of runners by country and state
More than 23,000 people from around the world set foot on Boston Marathon's 26-mile long race before the explosions shut down the internationally-celebrated event. So where did all these competitors come from?
GlobalPost produced the charts below that visualize the largest US states and countries represented at the 2013 Boston Marathon. Hover over a bubble for more information.
UPDATE: 4/16/13 1:30 PM ET
In case you missed it earlier, President Obama addressed the nation. Watch:
UPDATE: 4/16/13 1:15 PM ET
One of the victims of the dual explosions yesterday was identified as 8-year-old Martin Richard, of Dorchester. Two of the five members of his family were also seriously injured in the blast.
Martin was there to watch his father, William Richard, finish the 26.2-mile race.
"Little Martin gave his father a warm hug after he crossed the finish line — a tender moment that would be their last," wrote The New York Daily News.
Martin's father released a statement on Tuesday afternoon saying:
My dear son Martin has died from injuries sustained in the attack on Boston. My wife and daughter are both recovering from serious injuries. We thank our family and friends, those we know and those we have never met, for their thoughts and prayers. I ask that you continue to pray for my family as we remember Martin. We also ask for your patience and for privacy as we work to simultaneously grieve and recover. Thank you.
A second victim was identified as Krystle Campbell, a 29-year-old resident of Medford. The Atlantic Wire reported that the third victim is also thought to be a woman, but there are no further details at this time.
UPDATE: 4/16/13 1:01 PM ET
Prime Minister Benjamin Netanyahu describes Boston Marathon a "day of terror"
Following are excerpts from Prime Minister Benjamin Netanyahu's remarks made at President Shimon Peres' Independence Day reception for the foreign diplomatic corps on Tuesday:
"Yesterday, a day of enjoyment in Boston was turned into a day of terror. We send our condolences to President Obama, the American people and the bereaved families. On this day and on any day, Israel stands shoulder-to-shoulder with the American people. We are partners in freedom and in seeking a better future for all humanity.".
President Peres hosted a reception for the foreign diplomatic corps in Israel and expressed his condolences regarding the tragic events in Boston.
– From GlobalPost's Noga Tarnopolsky based in Jerusalem, Israel.
UPDATE: 4/16/13 12:45 PM ET
Explosives were in pressure cookers
A source briefed on the Boston bombings said the explosives used yesterday were in 6-liter pressure cookers placed in black duffel bags.
The person said the explosives contained metal shards, nails and ball bearings and were placed on the ground.
The person, speaking on condition of anonymity, told the Associated Press that law enforcement officials did not yet know what was used to set off the explosives.
The Boston Globe reported that the roommate of a Saudi Arabian man whose apartment was searched by investigators doubted he played a role in the bombing.
"I don't think he could do that," the roommate told the Globe.
"The Saudi Arabian man is at Brigham and Women’s Hospital in Boston, apparently being treated for injuries following the double bombing at the finish line on Boylston Street Monday afternoon," said the Globe.
Officials said Tuesday that the Saudi national was being regarded as a witness, not a suspect, according to The Washington Post.
He is reportedly in his 20s and is in the United States on a Saudi scholarship to study at a Boston university.
"We’re not aware of any Saudi suspect or Saudi person of interest," said a Saudi official at the embassy in Washington. The official added that the injured Saudi national was cooperating with investigators and had granted permission for his apartment to be searched.
"He volunteered to have it searched," said the official, according to The Post. "He is fully cooperating with authorities."
UPDATE: 4/16/13 12:34 PM ET
South Koreans have expressed shock over the bombing
President Park Geun-hye offering condolences and sympathy to President Obama.
Some US conspiracy theorists have blamed North Korea for the bombings. "It's a bit suspicious when North Korea stated they will do something to America on that day," wrote one anonymous user on Yahoo! Answers.
However, South Koreans, who have dealt with war rhetoric on a weekly basis, don't agree. Two Seoul residents said any suggestion that North Korea is behind the Boston bombing is nonsensical. "They simply wouldn't do that," said Inhye Yoon, a university student studying North Korean politics in Seoul. "They wouldn't plant a bomb in America. They would do that in South Korea or Japan."
- From GlobalPost's Geoffrey Cain in Seoul, South Korea.
UPDATE: 4/16/13 12:11 PM ET
Grassroots #HandsOverHearts London Marathon campaign in show of Boston support
In the wake of the Boston bombings, London police are amping up security in advance of both Sunday’s marathon and Margaret Thatcher’s funeral procession Wednesday.
Officials and event organizers insisted that Sunday’s marathon will not be cancelled.
"The police will be taking every possible precaution to make sure that both the funeral and the marathon at the weekend go ahead in the normal way," London Mayor Boris Johnson told the Telegraph.
“We fully expect that Sunday’s race, Registration and associated events will go ahead as originally scheduled,” said a statement posted on the website of the Virgin London Marathon. “We are currently reviewing all our security arrangements with the Metropolitan Police and we will post the latest information on all the events.”
"These are balanced judgments but we are absolutely confident here that we can keep the event safe and secure,” Hugh Robertson, Minister for Sport, said on BBC Radio 4. “I think this is one of those instances where the best way to show solidarity with Boston is to continue and send a very clear message to those responsible that we won’t be blown off course.”
Prince Harry, the patron of the London Marathon Charitable Trust, is still scheduled to present medals to the winners Sunday, as he did last year.
Meanwhile, a campaign began Tuesday to get London’s runners to show their support for Boston.
Lucy Fraser-Macnamara, a 27-year-old Londoner who is running the marathon to raise money for New Horizon Youth Centre, put out a call on Twitter using the hashtag #HandsOverHearts to get fellow runners to cross the finish line Sunday with their hands over their hearts in a public show of tribute to Boston.
The idea came to her on her bicycle ride to work Tuesday morning.
“The events in Boston yesterday really affected me and I was left feeling so low and wounded,” she told Global Post. “The thought of mums and dads, sons and daughter, brothers and sisters all there waiting proud for their loved ones and the moment of achievement snatched away from 25,000 runners brought me to tears.”
“Running is a solitary sport, yet as runners we are greater than the sum of our parts,” she wrote in an email. “It’s not a huge gesture but it will be to each and every runner that takes part.”
- From GlobalPost's Corinne Purtill in London.
UPDATE: 4/16/13 12:05 PM ET
People, cities, sports teams #PrayforBoston
Almost immediately following the bombings on Monday, photos, videos, and text messages streamed across phone, computer and television screens alerting the world to the unexpected horror that had just taken place.
Soon after that came an overwhelming wave of love and support from individuals, cities, and sports teams — and even an astronaut in space — all of whom rallied behind the common phrase: "#PrayForBoston"
See more of the support for Boston from around the world here.
UPDATE: 4/16/13 11:46 AM ET
European figures comment on Boston Marathon bombings
Italian Prime Minister Mario Monti, in a message to President Barack Obama, condemned the attack as a "a cowardly act of violence that prompts disdain and leaves us shocked with its suffering and horror."
"I am sure that even in these painful circumstances, America will know how to react by reaffirming the fundamental values of its great civilization," he said in a message posted on the government website.
"Faced with the cowardly and barbarous act, the American people can count on our total solidarity," French Foreign Minister Laurent Fabius wrote in a note to Secretary of State John Kerry.
Some took to Twitter:
Swedish Foreign Minister Carl Bildt:
Ethiopian running legend Haile Gebrselassie:
UPDATE: 4/16/13 11:40 AM ET
Pres. Obama addresses nation
"This was a heinous and cowardly act," President Obama said, addressing the nation at approximately 11:30 a.m. He was very clear in defining the explosions as terrorism. "The FBI is investigating it as an act of terrorism."
"Any time bombs are used to target innocent civilians, it is an act of terrorism," he said. "The American people refuse to be terrorized."
What we still don't know, Obama said, was whether a group or a "malevolent individual" was behind the attack.
"We will find who harmed our citizens and bring them to justice," said Obama. He added that the explosions showed how America responds to evil: "Selflessly, compassionately, unafraid."
Obama also urged the public to act, saying, "If you see something suspicious, speak up."
UPDATE: 4/16/13 11:28 AM ET
Mexico President addresses Boston Marathon
Mexican President Enrique Peña Nieto was quick to issue a statement of consolation and support after the bombings. And news of the attack led the broadcast news and newspaper front pages, with reports noting that none of the Mexicans participating in the race had been injured and that the bombing would not derail President Obama's planned visit to Mexico City in early May.
Beyond that, immediate reaction has been generally muted so far. Reaction here to such events, including the 9/11 attacks on the World Trade Center, has often been tinged by the complex view many Mexicans have of their powerful northern neighbor.
A political cartoon titled The Bostonian in Reforma, Mexico City's leading newspaper shows Secretary of State John Kerry, in colonial military garb, looking through a telescope at North Korea while a gloved hand slips a lighted stick of dynamite into his back pocket.
- From GlobalPost's Dudley Althaus in Mexico.
UPDATE: 4/16/13 11:05 AM ET
Indians express sympathy
With a significant Indian community and a large number of colleges that attract Indian students, Boston is close to the heart of many English-speaking Indians, who expressed their dismay on Twitter and Facebook as they woke up to the news of the bombings this morning.
Prime Minister Manmohan Singh strongly condemned the attack as a "senseless and cowardly act."
"The people of India join me in condemning the attack in the strongest terms. We stand in solidarity and sympathy with the bereaved families, the injured and the people of the United States," Singh said.
Despite local sympathy for the Boston victims, some Twitter users sniped that Singh's expression of solidarity, however appropriate under the circumstances, came much more swiftly than his tardy acknowledgement of December's brutal Delhi gang rape.
Coincidentally, Indian finance minister P. Chidambaram will deliver an address on the theme "Rise of the East: Implications for the Global Economy" at Harvard today.
No doubt he will diverge from the script to acknowledge the tragedy and, perhaps, he may speak briefly of his own experience fighting terrorism in India, where he was made home minister after his predecessor resigned following the November 2008 Mumbai attacks.
India put its embassy in Washington and the consulate general in New York on alert following the bomb blasts.
Foreign Minister Salman Khurshid told reporters here that there is no reason for Indians to be concerned about their relatives or Indian assets in Boston on Tuesday, remarking, "Our Finance Minister will also be in the Boston area and I am sure that he will have the opportunity to look at whatever briefings are there necessary locally. And I will remain in touch with him as well."
- From GlobalPost's senior correspondent in New Delhi, India, Jason Overdorf.
UPDATE: 4/16/13 10:30 AM ET
FBI press conference: UPDATES
The latest numbers stand thus: 176 people were injured and treated at area hospitals. 17 people are still in critical condition. The death toll remains at three.
Massachusetts Gov. Deval Patrick called the bombings an "act of terror" and reiterated that "two and only two devices were found yesterday."
Patrick said, "Everyone should expect continued, heightened police presence," in Boston, and encouraged Boston residents to be vigilant.
Boston Mayor Thomas Menino said, "Yesterday, terror was brought to the city of Boston."
"Let's keep working together. Let's offer a helping hand," said Menino. "Here we know our neighbors, and we grieve for [the victims]. We know our heroes too..."
Sen. Elizabeth Warren, the Democratic senator from Massachusetts, said, "We want to thank those from all around the country and all around the world whose prayers have poured in."
"Boston will survive," she added.
FBI Special Agent Richard DesLauriers said it remained a "very active investigation" but there were "no known additional threats."
Boston's police commissioner called the site of the explosions the most complex crime scene in the department's history. He said the 15-block crime scene had been reduced to 12 blocks today and will continue to collapse.
The superintendent of the police said the public should expect to see an enhanced presence of city and state police and the National Guard, offering comfort to the citizens of Boston.
"This will be a worldwide investigation," said DesLauriers. "We will go to ends of the earth to find those responsible for this despicable crime."
The authorities thanked first responders and brave bystanders for their help, asked people to come forward with information, photos or videos from the event and asked for the public's patience as the crime scene was processed.
UPDATE: 4/16/13 9:25 AM ET
Heavy security in Boston; FBI press conference
The BBC tweeted this picture of the heavy security presence in downtown Boston.
The FBI will hold a press conference at 9:30 a.m. Watch below:
UPDATE: 4/16/13 9:05 AM ET
South Africa condemns bombings
South Africa's ruling party, the African National Congress, released a statement about the Boston Marathon explosions condemning "the senseless and dastardly act of terrorism that happened in Boston which was unleashed to unsuspecting and innocent international athletes, dignitaries, spectators and the community of Boston who participated in the annual race."
The statement read:
There can be no justification for such a despicable attack that claimed three lives and injured 130 people including kids, it deserves to be condemned by the world community.
We welcome the speedy response of the South African Department of International Relations and Cooperation in supporting the two South Africans who were injured in the blast and continued liaison with the 26 others who took part in the race.
We call on the government of the United States of America to do everything in its powers to bring to book those that are responsible for this terror act.
We also call on the world community under the auspices of the United Nations to join hands in the fight against terrorism. We extend condolences to the families of the deceased and wish speedy recovery to the injured.
UPDATE: 4/16/13 8:22 AM ET
Law enforcement officers investigating the Boston Marathon bombings searched an apartment in the Revere neighborhood about 10 miles from the attack site early on Tuesday.
As the FBI took over co-ordination of a "potential terrorist inquiry" into the dual bombings that killed three and wounded more than 140, Boston police canceled all leave and urged the city's residents to stay indoors and avoid large groups.
Commuters in Boston and surroundings were warned their bags would be searched on Tuesday morning as the city remained on high alert.
Read more here.
UPDATE: 4/15/13 11:40 PM ET
As April 15 comes to a close in Boston, this is what we know
Dead: Three, including an 8-year-old boy
Wounded: At least 140, according to local media. Various outlets report at least 100 and as many as 144 injured.
The front page of the Boston Globe's website updated throughout the evening as the toll of dead and injured rose:
How many blasts: At least 2; fire at JFK library probably an unrelated incident. NBC said of the explosives:
"Officials have told NBC News that the devices detonated were homemade, crudely assembled, and possibly had shrapnel added to them for added harm after the blasts."
How many explosive devices found: In dispute. It's been reported as many as five additional devices may have been defused by security crews after the initial blasts, but officials have since said they doubt the devices were bombs.
Who did it? We don't know yet. Police have said repeatedly in the course of the day that while they have questioned many people, they do not yet have a suspect in custody. Many observers have posited that either an international or domestic terrorist group may have been responsible, though none has claimed responsibilty. Rampant rumors circulated earlier alleging that a Saudi national may have been in custody as a suspect, leading to an unfortunate outbreak of high-profile hate speech.
What the authorities are doing: The FBI has taken over the investigation from the Boston Police Department.
“It is a criminal investigation that is a potential terrorist investigation,” Richard DesLauriers, the head of the FBI in Boston, told reporters.
Police officers remain in full force:
Who to call: Family members seeking information about relatives should call (617) 635-4500. Those with information that might help the investigation can call 1(800) CALL-FBI or the BPD’s Crime Stoppers Tip Line at 1 (800) 494-TIPS.
When will we know more? The FBI has sceduled a press conference for 9:30 a.m. on Tuesday at the Westin Hotel.
UPDATE: 4/15/13 11:35 PM ET
"At that moment, everything stood still"
GlobalPost Americas Editor Alex Leff interviewed witnesses of the blasts in Boston today. Listen here:
UPDATE: 4/15/13 11:04 PM ET
France, UK on edge after Boston blasts
In reaction to the twin blasts in Massachusetts, early Tuesday local time French Interior Minister Manuel Valls called on local officials and security forces nationwide "to reinforce without delay the presence of patrols," Agence France-Presse reported.
Officials in London, meanwhile, are reappraising security measures ahead of their own city's internationally-attended marathon, planned for this coming weekend.
UPDATE: 4/15/13 10:35 PM ET
Amid outpouring of support, a tiny minority hangs on to hate
Today has been a day that has tried the soul of a city.
In the hours since the two explosions rocked the streets of Boston, messages of love and support have saturated the internet — but these inspiring and compassionate posts were not universal.
In fact, the commentary streaming across the Twitter feed of the Westboro Baptist Church was both hostile and hateful.
The Westboro Baptist Church, based in Topeka, Kansas, is a small, virulently homophobic, anti-Semitic group that regularly stages protests or pickets institutions and individuals they think support homosexuality or otherwise subvert what they believe is God’s law.
WBC even protested the funerals of children who were slain in the horrific Newtown shootings this past December.
Read the rest of this story here.
The day's dominant sentiment, however, couldn't have been more different. GlobalPost's Kyle Kim, who was at the site of the explosions after they occured, summed it up with a quote from beloved children's television personality Mr. Rogers:
UPDATE: 4/15/13 10:05 PM ET
Boston Police Commissioner Edward Davis, while holding a second press conference today, said no suspects are in custody.
Also speaking at the conference, Massachusetts Gov. Patrick said more than 100 people were injured, some gravely, according to the BBC.
Estimates from area hospitals have said as many as 130 were treated for injuries.
Patrick said that while Boston would be "open" on Tuesday, there would be "a heightened law enforcement presence."
"There will be random checks of backpacks and other parcels. We are also asking that everyone be on a state of heightened vigilance," he said.
The Wall Street Journal cited an official saying counterterrorism officials found five other suspect devices, but doubted that they were bombs.
The devices were initially thought to be undetonated explosives.
GlobalPost's Kyle Kim saw this scene earlier in the day:
UPDATE: 4/15/13 9:29 PM ET
Inside the ER
A first-year resident at Brigham and Women's Hospital who was inside the emergency department as victims were rushed there earlier today spoke to GlobalPost this evening.
The resident, who doesn't work in the emergency ward typically, happened to be there this afternoon when victims were brought in. The department and trauma surgeons there quickly mobilized to receive victims, he said.
"Everybody was on their feet," the resident said.
He added that the hospital was quickly locked down as patients were rushed in. "The ATF showed up. There were lots of cops around," he said. "The only way in was through an ambulance.... The only way out was through the front door."
The injured were also sent to Massachusetts General Hospital, Boston Medical Center, Beth Israel Deaconess and Tufts Medical Center, the Wall Street Journal reported. The journal said the largest number of victims, 26, were being treated at Brigham and Women's.
UPDATE: 4/15/13 9:15 PM ET
3 people are confirmed dead
Police have said three people were killed by the explosions today. The count of injured continues to grow, with some outlets reporting over 140 injured.
UPDATE: 4/15/13 8:25 PM ET
Latest reports say more than 130 injured
CNN cites area hospitals as saying at least 132 people were injured in today's blasts. The count included eight children.
It was reported earlier that at least two died from the explosions, including an 8-year-old boy.
UPDATE: 4/15/13 6:55 PM ET
Massachusetts Gov. Deval Patrick Responds to Boston Marathon Explosion
"This is a horrific day in Boston. My thoughts and prayers are with those who have been injured. I have been in touch with the President, Mayor Menino and our public safety leaders. Our focus is on making sure that the area around Copley Square is safe and secured. I am asking everyone to stay away from Copley Square and let the first responders do their jobs." (Source: TIME)
UPDATE: 4/15/13 6:40 PM ET
Video timeline of the incident and aftermath
Browse our timeline of videos of the incident and aftermath, here.
The explosions and aftermath were also closely followed on social media.
So far two people have been reported killed, with anywhere between 80 to a hundred people injured. NBC News reported that law enforcement officials confirmed one of the two people killed in the explosions to be an eight-year-old.
The White House has labeled the explosions an "act of terror" according to an official cited by Bloomberg.
UPDATE: 4/15/13 6:21 PM ET
Obama speaks briefly
President Obama carefully reiterated that "we don't yet have all the answers," but stressed that "we will find out who did this and we will hold them accountable."
"On days like this, there are no Republicans or Democrats," he said, saying there are only concerned people.
Earlier, Boston Mayor Thomas Menino said authorities were coordinating to set up centers for people looking for loved ones running in the marathon.
"It's a very serious time so we need people to stay away from the area."
The 15-block area around the blast site will be closed until further notice. The police said there was no specific intelligence about this incident happening.
The police said there were no suspects in custody, contradicting earlier widespread reports about a "person of interest" in custody.
UPDATE: 4/15/13 6:00 PM ET
Obama addressing the nation
President Barack Obama will address the nation at 6:10 p.m.
UPDATE: 4/15/13 5:40 PM ET
Reports of 'person of interest' being taken into custody
Fox News and several other outlets are reporting that a "person of interest" has been taken into custody:
UPDATE: 4/15/13 5:32 PM ET
Third explosion was electrical fire
The third explosion reported at the J.F.K. Library at the University of Massachusetts was confirmed by police. They said it was caused by an electrical fire and believed there was no connection to the other explosions near the finish line.
A law enforcement official told the Associated Press that cellphone service had been shut down in the Boston area to prevent remote detonation of explosives.
Massachusetts General Hospital is taking care of 22 patients from the explosions, with six in critical condition, according to Bloomberg.
UPDATE: 4/15/13 5:18 PM ET
Searching for a suspect
The police scanner from the scene said Boston police are looking for "A black man with a black backpack and a black hoodie" who was denied access to the Fairmont Copley Hotel, five minutes before the bombing.
When he was stopped by security, he pulled his hood up and left.
Military Beth Israel Deaconess hospital on Francis Street is requesting that police check out a military style backpack left at their emergency room. Police indicate that they have one airport style bomb dog, but no more Explosive and Ordnance Disposal teams available.
A hundred people have been injured and/or treated in four area hospitals in Boston, according to WBUR.
A site has already been set up for people to find missing loved ones in the area. It's called Safe & Well. Google has also set up a person finder here.
The Boston police are also seeking blood transfers from Rhode Island.
On a heartrending note, the last mile of the Boston Marathon was dedicated to the victims of the Sandy Hook Elementary shooting in Newtown last December.
"In the first twenty miles we're honoring the twenty Sandy Hook first graders," Laura Nowacki, a spokesperson for Newtown Strong, told WBUR Boston. "When we crest Heartbreak Hill, and we're coming back towards Boston, we run the final six for our six fallen educators, including their lives, to protect our children."
UPDATE: 4/15/13 5:00 PM ET
New York, D.C. ramp up security
New York City and Washington, D.C. have increased their security in the wake of the Boston explosions.
"We've stepping up security at hotels and other prominent locations in the city through deployment of the NYPD's critical response vehicles until is more about the explosion is learned," Deputy Commissioner of the New York Police Department Paul J. Browne told CNBC.
Officials also told NBC News that security had been increased around the White House.
The Federal Aviation Administration also ordered a no-fly zone over the site of the explosions in Boston.
According to the Associated Press:
The agency said in a notice issued Monday about an hour after the explosions that a no-fly zone with a 3.5-mile radius has been created over 811 Boylston Street. The zone is limited to flights under 3,000 feet in altitude, which is lower than most airliners would fly except when taking off or landing.
UPDATE: 4/15/13 4:50 PM ET
Runners dazed and confused (VIDEO)
GlobalPost's Alex Leff sent this video from the corner of Commonwealth Avenue and Fairfield Avenue, a few blocks from the blast. Runners in the Boston Marathon were leaving the premises as police and emergency crews secured the area.
UPDATE: 4/15/13 4:40 PM ET
Video of aftermath
Our correspondent near the scene, Alex Leff, said the police are not letting reporters close to the site of the explosion.
This video from The Boston Globe shows the immediate aftermath of the explosion:
UPDATE: 4/15/13 4:25 PM ET
Another explosion was confirmed at the J.F.K Library. It is not yet clear if it was a controlled explosion. The Associated Press cited an intelligence official saying there were two more devices found at the marathon currently being dismantled.
Here is a map of the current locations with suspected or exploded devices:
View Boston Marathon Explosion in a larger map
UPDATE: 4/15/13 4:15 PM ET
Tense situation on the ground
Peg Carter, of Middleborough, came to see the marathon because her 28-year-old daughter was running. She was watching it with her 15-year-old step son. She told GlobalPost's Alex Leff that she heard the blast.
"It was huge. It sounded like a canon. It happened at the 26th mile. Somebody screamed that it was a terrorist attack. I've got a scary feeling that a lot more of these will go off."
A lot of people on Commonwealth Ave were discussing the possibility of a third device. Many congregated while police were trying to get spectators to head home. Police were chasing people away from the scene. There was tension in the air as police tried to keep the area clear, said Leff.
UPDATE: 4/15/13 4:05 PM ET
BOSTON — At least two explosions hit near the finish line of the Boston Marathon on Monday afternoon. Boston Police have confirmed two dead and twenty-three injured.
Witnesses reported hearing the explosion just before 3 p.m., according to MyFoxBoston.com.
"There are a lot of people down," said one man, according to the Associated Press.
Another device was reportedly found near the Mandarin Hotel, according to the police scanner. The scanner also indicated the presence of another abandoned package in front of Eastern Standard in Kenmore Square. A perimeter is being established around Eastern Standard.
The Marathon is now over. Runners are being routed to Boston Common.
The police have reportedly asked for K-9 bomb dogs to sweep the area and Boylston "before we can put our officers there."
A command post is being set up in The Westin Copley Place Hotel, in Copley Square. Another suspected device has reportedly also been found at the J.F.K. Library at the University of Massachusetts.
Our correspondent on the scene, Alex Leff, said it was a tense evacuation scene, with sirens and police telling pedestrians to keep walking and return to their homes. Runners were walking in shock, dumbfounded.
Leff reported an explosion going off. The police scanner said a controlled explosion was set to detonate a suspected device at 600 Boylston.
GlobalPost's Kyle Kim is also near the scene:
President Barack Obama has reportedly been notified of the explosions, according to Bloomberg.
Here is a Vine of when the explosion happened:
And raw footage of the scene of the explosions:
Here is live video from the scene, via CBS:
Boston Marathon Finish Line
Here is the reaction on Twitter: